Hello. I would like some assistance, as I am having an issue with KDE on reboot. Whenever I run it off my LiveUSB - and I haven't installed it yet, although I am running 18.3 Cinnamon - I get a "CPU Lockup" at shutdown. Basically, after I choose "reboot" in the options menu, It sends me to a CLI signin, but I can't type anything. After a few seconds, it says "CPU #X [and then something about a bug and locking up, sorry I can't remember the exact words]". Then I have to hard shutdown.
Specs (Taken from Cinnamon which is my primary, not KDE):
System: Host: steven-GL753VE Kernel: 4.13.0-32-generic x86_64 (64 bit gcc: 5.4.0)
Desktop: Cinnamon 3.6.7 (Gtk 2.24.30) dm: lightdm
Distro: Linux Mint 18.3 Sylvia

"A computer is like air conditioning. It becomes useless when you open Windows."
- Linus Torvalds

I would discourage you from going towards KDE while you are running Mint. Reason: the Mint team intends to drop the integrated Mint-KDE distro/iso when Mint-19 comes out. While I absolutely believe that KDE has the most power and features of all the DE's I've used, most of the Mint-KDE users are in the position of looking for another DE or another Linus distro with embedded KDE. In other words, there is a future for Mint-KDE users, but it's just not very bright. If you think Mint is a distro you want to stay with you might be better off adjusting to another DE before you get any further with KDE (and it's starting to look like Cinnamon is the DE the Mint team intends to continue to develop and support for the long term).

HERE is a thread that may give you a little more insight into the KDE situation.

“I think that this situation absolutely requires a really futile and stupid gesture be done on somebody's part!""We're just the guys to do it.”Animal House